Insulated light transmitting panel



Dec. 19, 1967 M. n. COOPER, JR., ETAL ,3

INSULATED LIGHT TRANSMITTING PANEL Filed Aug. 25, 1965 E7 v YINVENTOR.Mew/e 0. 'oopem/z:

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United States Patent v O INSULATED LIGHT TRANSMITTING PANEL Merle D.Cooper, Jr., Leavenworth, Kans., and Kenneth M. Blom, Kansas City, Mo.,assiguors to Butler Manufactoring Company, Kansas City, Mo., acorporation of Missouri Filed Aug. 25, 1965, Ser. No. 482,397 3 Claims.(Cl. 52-202) ABSTRACT OF DISCLOSURE A light transmitting, heatinsulating panel construction for use in buildings employing a first,outer, light transrnitting plastic sheet having partial majorcorrugations in the side edges thereof which permit side edge engagementof the sheet with the side edges of building panel sheets of likeconfiguration, and an inner, second, light transmitting plastic sheetalso substantially rectangular in shape, the second sheet of both lesserlength and width than the first sheet, with upwardly dished side and endedges thereon, the upper extremities of the side and end edges of thesecond sheet bonded to the under surface of the first sheet insubstantially continuous manner, the side edges bonded closely adjacentor within the inner margins of the partial side edge corrugations of theouter sheet and the end edges bonded inwardly spaced of the end edges ofthe outer sheet.

This invention relates to improvements in fiber reinforced plasticpanels usable for various structural purposes such as skylights,partitions, awnings, canopies, wall and ceiling elements, etc., andrefers more particularly to such panels having integral therewith meansfor insulating portions or substantially the entirety thereof.

The Hungerford et al. application Ser. No. 146,479, filed Oct. 20, 1961,now Patent No. 3,265,556, Fiber Reinforced Plastic Panel and Manner ofMaking Same, discloses a typical glass fiber reinforced thermosettingresin panel to which the instant invention is particularly adaptable.

It is well known to provide double layer windows, windshields, glazingunits, storm Windows, observation ports, skylights, heat and soundinsulating units, and the like. Such structures may be opaque, in Wholeor in part, translucent in whole or in part, transparent in whole or inpart or combinations thereof.

In the patents to Hield et al. 2,815,831, issued Dec. 10, 1957, Columnand Rafter Assembly for Rigid Frame Buildings, and Simpson et al.2,871,997, issued Feb. 3, 1959, Low Pitch Rigid Frame Building, theremay be seen the manner of mounting, in rigid frame buildings, roof andside wall panels on the structural framework.

It has become quite common to substitute, for one or more lengths ofpanel members of such roof or side wall panels or panel arrays, one ormore longitudinal, transverse or both, like configured translucent ortransparent skylight or light transmitting panels (like configured tothe panels with which they mesh) such skylight or light transmittingpanels typically of reinforced plastic of the type disclosed in theHungerford et al. application, supra.

However, in such use, and particularly in roof applica tions forskylights, when the outside atmosphere is relatively cold and the insideatmosphere of the building is relatively warm, there arises the problemof condensation on the inner faces of the panels with concurrent andconsequent sweating and dripping therefrom. Condensation within abuilding, thus takes place when the temperature of the inside surface ofa given panel arrives at the dew point within the building, which meansthat the outside cold has passed or crept through the single layerpanel.

Thus, there arises the situation, typically and very commonly, in abuilding of the type described, namely, one utilizing interleaved oroverlapping flat metal panels for roof panels, of a single, series, setor array of skylight panels being interleaved in the roof panels to givegreater light, same not having the conventional glass fiber insulationor the like thereunder whereby the warm air of the interior of thebuilding strikes directly against the chilled panel, thus resulting incondensation, dripping, sweating, etc. When one corrects this byinsulating the underside of the panel as may be done with the metalpanels by using conventional insulation with a vapor barrier, naturally,all skylight and illumination effects desired will be lost,

To obviate this, that is, to obtain the benefits of insulation, whileretaining the advantages of skylight light transmission, it has becomecommon to insert sky domes in such metal panel roofs. A typical suchdome may be seen in Bettcher 2,918,023. In such construction, a curbingis inserted into an opening in the roof which is then topped off with amultiple layer translucent or transparent level of glass, plastic sheet,or the like. Difficulties with this construction in general involve theundesirability of breaking the roof line, the extra work, time,materials, special parts, etc., required to insert such sky domes, theloss of the well-known advantages of panel edge-to-panel edge juncturein the regular manner of the metal panel-to-panel connections, bothlaterally and longitudinally of the roof, the fact that, when one breaksthe roof line and provides a number of seams, both vertically andhorizontally, additional leak problems arise, additional problems ofinsulation, that is, heat loss from the interior of the building, etc.

Summary of the invention An improved plastic panel for wall and roofconstruction, particularly in skylight use in rigid frame buildings. Aninsulated translucent or transparent plastic panel configurationparticularly utilizable as a skylight in buildings having interleavedmetal panels for side and end walls and roofs, which light transmitingpanels are of the same configuration as the panels they are used inconjunction therewith, whereby to retain the wall or roof line. Meansfor insulating the interior surface of roof and wall translucent andtransparent plastic panels to avoid condensation, sweating and drippingwith respect to same due to temperature differences between the outsideand inside of the building. A light transmitting roof panel constructionutilizing two separate spaced translucent and/or transparent panelswherein improved light dispersion is achieved, together with insulationof the outer of the two of said panels.

An object of the invention is to provide an improved plastic panel usedfor wall'and roof construction, particularly in rigid frame buildings,and most particularly in skylight use.

Another object of the invention is to provide an insu lated translucentor transparent plastic panel particularly usable for skylightconstruction, which panel retains all of the advantages of anoninsulated plastic panel for skylight purposes, while offeringadditional advantages with respect to avoidance of interiorcondensation, sweating and dripping.

Another object of the invention is to provide an insulated, configured,fiber-reinforced plastic panel particularly utilizable as a skylight inbuildings having inter leaved metal panels for side and end walls androofs, which light transmitting panels are of the same configuration asthe panels they are used in conjunction therewith whereby to retain thewall or roof line, yet such panels obtaining and providing many andcomplete benefits of insulation without losing the majority of theirbenefits of light transmission.

Another object of the invention is to provide' such an insulated lighttransmitting panel for use in panel walled buildings wherein the sideedges and end edges of a configured translucent or transparent plasticpanel are left free for interleaving or interengagernent with other likelight transmitting configured panels or rnetal panels, the centralportions thereof fully and completely insulated whereas to eliminatecondensation, sweating and dripping thereon.

Another object of the invention is to provide means, products andmethods for insulating the interior surfaces of roof and walltranslucent and transparent plastic panels whereby to avoidcondensation, sweating and dripping with respect to same due totemperature differences between the outside and inside of the building,such products, methods of manufacture and structures simple,inexpensive, easily obtained, yet dependable and long lived in use,application, etc.

Yet another object of the invention is to provide such insulated lighttransmitting panels wherein end and side edge portions and centralportions thereof may be left in condition for engagement with other likepanels or interleaving metal panels of a side or end wall or ceilingarray of building skin panels, while retaining the desired flexibilityfor support by interior building structurals, connection to the otherpanels, etc.

Another object of the invention is to provide a light transmitting roofpanel construction utilizing two separate spaced translucent and/ortransparent panels wherein improved light dispersion is achieved becausethe double panel breaks up, diff-uses or disperses light rays to agreater extent than a single panel construction.

Other and further objects of the invention will appear in the course ofthe following description thereof.

In the drawings, which form a part of the instant specifioation and areto be read in conjunction therewith, an embodiment of the invention isshown and, in the various views, like numerals are employed to. indicatelike parts.

FIG. 1 is a three-quarter perspective view from below of a corrugatedplastic light-transmitting panel having the inventive improvement on theunderside thereof.

FIG. 2 is a side elevation of a roof construction showing the panel ofFIG. 1 supported on transverse roof purlins and engaging with the endsthereof the ends of conventional insulated metal roof panels.

FIG. 3 is 'a view taken along the line 3--3 of FIG. 2 in the directionof the arrows.

Characterizing the panel of the drawings, that is, the basic translucentor translucent or transparent glass fiber reinforced plastic corrugatedpanel, its cross-sectional form is typically that of the U5. HieldDesign Patent 178,659, issued Sept. 4, 1956, or l-Iield Design Patent178,605, issued Aug. 28, 1956, Building Panel. The form actually shownis the latter. This comprises an elongate rectangular panel 9 having endedges 10 and 11 and side edges 12 and 13. The upper or outer side of thepanel 14 is opposed by the lower or inner side of the panel 15. Thepanel is configured in transverse cross section to have a pair ofcomplete major corrugations 16 and 17 extending upwardly therefrom withstepped bases 16a and 17a. Elongateminor corrugations 18-23, inclusive,are positioned in pairs between the major corrugations 16 and 17 and thelatter and partial side edge corrugations 24 and 25. The latter fit overlike partial major corrugations to make a side edge connection with alike sheet of either metal of plastic (preferably metal). It isimportant to note that the side edge partial major corrugations 24 and25 have a stepped base 24a and 25a, respectively. It is contemplatedthat the minor corrugations 18-23; inclusive, are not essential for thepractice of the instant invention, indeed, they are added complicationsthereto, but elongate corrugation of the nature of corrugations 16 and17 would be generally expected in building panels for strength andrigidity, while the presence of the partial side edge corrugations 24and 25 with their stepped bases 24a and 25a are well nigh essential tothe instant invention.

General requirements of corrugated plastic panels of this type as usedfor skylights would be that both surfaces thereof should be smooth andfree of wrinkles and other defects. The panels should conform to theshapes, dimensions and tolerances as shown on applicable productdrawings. The primary use of such plastic panels should be forflush-mounted installation on roofs of prefabricated metal buildings, asseen in FIG. 2, the function of the panels being to permit the entranceof light into the building. Such panels would typically be used inconjunction with galvanized steel, aluminized steel or aluminum panelsof the same configuration to form a weather-tight covering. Such panelsmay be used on side walls and end walls of the buildings and must beable to function in any position.

With respect to mechanical, chemical and other basic propertyrequirements, typically, the material would be a translucent, lightstabilized, thermosetting, acrylic modi fied, polyester resin with athoroughly impregnated glass fiber reinforcement. A typical resincomposition (100 parts total) would constitute no less than 15 partsmethyl methacrylate monomer and no more than 25 parts styrene monomerwith polyester accordingly. The glass fiber reinforcement, with anominal weight of two ounces per square foot of panel, would constituteat least 25 percent of the combined total weight of the resin and glassfiber reinforcement. The panels typically would Weight eight ounces plusor minus 10 percent per square foot. The color of the panel typicallywould be the standard skylight green. Color would be consistent not onlyWithin a shipment, but from any one shipment to any other ship ment. Theminimum visible light transmission would be 82 percent (air 100 percent)when measured in accordance with Federal specification LP 4063 Method3021. The maximum infra-red transmission would be approximately 60percent (air 100 percent) and ultra violet transmission shall be 3percent or under. The panels should not in any way react with metalpanels to produce discoloration, corrosion or any other unsightlycondition. The resin coating over the glass fibers shall typically becapable of withstanding no less than 1500 hours of weatherometer testing(ASTM D-22 Method) without evidence of glass fiber blooming, loss ofsurface gloss, or any other type of detrimental deterioration.

The panel typically is fabricated as a fiber-reinforced resin panelincluding a moisture impermeable corrosion resistant, extremely toughsurfaced layer which is permanently bonded to the panel and remains anintegral part thereof throughout the life of the panel. Such surfacelayer has an uninterrupted bond with the underlying resin body and itssmooth, glossy exposed face. To obtain this surface layer, there isplaced upon at least one surface of a sheet-like web, made up of acollection of reinforcing fibrous resin, a thin preformed film-like bodyof polyvinyl fluoride while the resin is still in liquid state, that is,before polymerization thereof has progressed to any appreciable degree.Such film-like body has a web contacting face treated to promoteadhesion with the resin as the latter is cured and further is laterallyheat shrinkable to substantially the same extent as the potentiallateral shrinkage of the resin impregnated Web during polymerization ofthe resin under the temperatures utilized in the curing of the panel.The composite uncured structures are then subjected to heat whilemaintaining the film-like body in firm but low pressure contact with theweb throughout substantially the entire area covered by the film-likebody. During the cure, the resin polymerizes and permanently bonds tothe film-like body and at the same time the film-like body contracts tothe same extent as t resin impregnated web.

The panel is typically formed from a bulk roll from which is unwound acontinuous web of glass or other reinforced fibers. Such web is composedof loosely interconnected or matted fibers and is highly porous. Suchweb typically has an uncompressed air thickness of approximately 0.048and 0.139 inch, the fibers having an average diameter on the order of 10microns and a length of 2 to 3 inches. The density weight of the web isbetween and 3 ounces per square foot. The width of the web is determinedby the width to be given to the final product and is selected inaccordance therewith.

As such web is unwound, it is passed into an impregnating trough whereit is immersed in a body of liquid resin to thoroughly impregnate same.Typical commercially available unsaturated polyester resins modifiedwith vinyl aromatic (styrene) or acrylic and vinyl aromatic monomers areemployed. If desired, various catalysts can be employed to aid in curingthe resin, such as catalysts of the organic peroxide type such asmethyl, ethyl, ketone peroxide, benzoyl peroxide, and tertiary butylperbenzoate. For speed in manufacturing, a resin composition whichpolymerizes to a hard, strong and solid mass within 20 to 60 minuteswhen subjected to temperatures of the order from 150 to 300 F. isemployed.

Pigments or dyes, relatively light, fast. and unaffected by thecatalysts, may be included in the resin trough to impart the desiredtint or color to the vinyl product.

Once the resin impregnated web has left the trough, it is fed directlyinto the nip of a pair of squeeze rolls which serve not only to squeezeexcess resin from the impregnated web, but also to firmly contact withthe opposite faces of the advancing, but still uncured web, a continuouslayer in the form of a preformed, thin (0.5 to 5 mils) film of polyvinylfluoride, known more familiarly under the Du Pont Company trademarkTedlar. Such film is drawn in continuous fashion from bulk rolls,passing from each roll into the nip of the squeeze rolls where it ismerged with the confronting face of the impregnated Web.

The film body must be substantially uniform in thickness and have apotential lateral shrinkability when subjected to the resin curingtemperatures and during the period of cure, substantially equal to thelateral shrinkability of the web. To promote adhesion between the filmbody and the web, the web contacting face of the film is provided with abond-promoting surface, such as by incorporating in said face, duringmanufacture of the film, microscopic irregularities into which the resinwill reach or, alternatively, forming a thin coating on said face oftitanium (IV) oxide by treatment with alkyl titanates and subsequentcontrolled hydrolysis thereof. Such polyvinyl fluoride films asdescribed are readily available from the manufacturer.

Subsequent to the contacting of the film bodies with the Web through thesqueeze roll, the laminated wet layup is passed to a conveyor or tablethrough shear blades where same is cut to desired lengths. Air bubblesor creases in the layup may be removed by manually wiping the laminatewith wire squeegees in a direction to expel air at the edges of thelayup and smooth out the films.

Lengths of uncured layup are then placed in stacked arrangement betweenupper and lower light-weight caul plates with each length between a pairof said plates to form a stack assembly. Such plates impart to the wetlayup the final cross-sectional configuration desired, such as seen inthe Hield design patents, supra, and obviously may be flat or in anyconfiguration. The stack assembly is then placed on an oven conveyor andpassed through the curing oven. While the speed of the oven conveyor andthe temperatures in the oven may be varied according to particularresins employed, the range in a typical process is from a low of 150 toa high of 300 F. through a period of from 15 to 60 minutes in the oven.As a particular example, using a web of the characteristics set forthearlier with an acrylic-modified polyester and a one- 6 mil polyvinylfluoride film, the temperature ranged from 200 F. to 300 F. with acuring time of 30 minutes.

Pressure may be applied in known fashion to the layup during the cure,but only suflicient pressure is required as to insure that the filmmaterial will be maintained in continuous contact with the web duringthe cure so that it will conform closely to the web. Maximum pressureshould be no more than 10 p.s.i. and preferably is much less, rangingfrom zero to 5 p.s.i. When the stack emerges from the curing oven, theplates are separated from the cured articles and the latter are nowready for use except as for such edge trimming as may be required toneaten the appearance and provide uniform edges.

In the completed construction of FIGS. 1 and 3, the bottom panel 26, asfixed to the upper panel 9, comprises a unitary structure which may bedescribed as follows. The upper panel 9 is rectangular in shape, aspreviously described, and has major and minor corrugations therein thelength thereof intermediate the side edges thereof, with partial edgecorrugations 24 and 25 bounding same. The lower integral panel 26comprises a molded elongate rectangular sheet formed into twosubstantially rectangular bubbles. These bubbles have elongate sideedges 26a and 26b which are attached at their upper extremities into thestepped base portions 25a and 24a of partial edge corrugations 25 and 24of upper panel 9. The end faces or extremities of the bottom panel 26,that is, the end faces of the two bubbles made up thereof, compriseelongate end panels 260 and 26d, respectively. These are bonded at theirupper extremities directly to the underside 15 of panel 9 betweencorrugations, major and minor. Polyethylene closures or plugs 27 aresealed into the major corrugations 16 and 17, including their steppedbases 16a and 17a, surrounded by a suitable adhesive or sealingsubstance of conventional type which bonds plug 27 to the upper panel 9and the end walls 260 and 26d. The said sealing substance is worked intothe minor corrugations 18-23 as small plugs to effect a seal between theupper panel 9 and lower panel 26. These minor corrugation seal pointsare seen at 28 in FIGS. 13.

The central connection as at 29 (FIG. 2) between the upper panel 9 andthe lower panel 26 is effected by a cross beam in the mold in which thelower panel is formed and effects a panel-panel seal at sanded upperpanel under surface zones between the major and minor corrugations.

There is thus effected a circumferential upper panel 9-lOWC-I panel 26connection which is continuous along the side edges of the lower panelon the underside of upper panelportions 24a and 25a and intermittent atthe ends 26c and 26d save for sealing substance inserts '28 and plugs27. There is only a partial seal between the upper and lower panelsalong the center portion 29.

The view of FIG. 2 shows a typical roof panel assemblage wherein theinventive panel overlies with its lower end the upper end of a metalpanel 30- of like configuration to upper panel 9 and having on theunderside thereof as at 31, conventional glass fiber insulation withconventional facing material underlying same, the latter operating toprovide a vapor seal and give a pleasing ceiling appearance. Likewise,to the right in FIG. 2, there is shown the lower end of a metal panel 32which overlies the upper end of panel 9 and has at 33 like conventionalinsulation and facing. Suitable conventional fasteners are employed atthe upper and lower end overlaps'of panel 9 and panels 30 and 32.

To the right and left in FIG. 3 there are shown the partial edgecorrugations of like configured metal panels 34 and 35 underlying edgepartial corrugations 25 and 24 of panel 9, respectively, in the roofpanel array. Suitable conventional fasteners are again employed throughthe crowns of the partial corrugations to connect adjacent roof panelsto one another.

Referring again to FIG. 2, transverse roof purlins 36, 37 and 38underlie and support panels 9, 30 and 32 with purlins 36 and 38underlying the end overlaps and purlin 37 underlying the central bubbledividing area 29 of under panel 26. The purlins 36-38, inclusive, arecarried in conventional fashion on rafter beams or members of the typeclearly seen in US. Hield Patent 2,815,831, and Simpson Patent2,871,997.

In the process of application of the glass fiber bubbles or lowersurfaces 26 to the upper panel 10, the following steps are employed:

(a) The bottom panel 26 mold, the upper receiving surface of which isconfigured to the desired shape (here a two bubble construction), isplaced adjacent a curing oven or on a conveyor feeding a curing oven.

(b) After removing a top protective film, an uncured resin impregnatedglass fiber composite is draped over the mold. A bottom film sheet,preferably of acetate, remains, against the mold face. However, thisfilm could be cellophane, Mylar, Tedlar or others.

(c) The pre-formed and pre-cured plastic top panel which has previouslybeen sanded at points of contact (ends, side edges and centrally) withthe wet layup placed on top thereof.

(d) A fixture which holds the plastic panels in position is then placedon top and the entire assembly is processed through the curing ovenwhere heat and a small amount of pressure are applied, whereby to curethe lower panel.

(e) After leaving the oven, the top assembly is removed and thecomposite panel structure according to the teachings of FIGS. 1-3,inclusive, is taken out of the mold and cleaned.

(f) Closures, preferably of polyethylene or the like (with a sealingsubstance or plastic glue on the top and bottom thereof) are installedin the major corrugations at each end of the panels. The sealingsubstance is worked by hand into the openings at the minor corrugationsat each end of the panel.

For the central bubble-panel seal, the pre-forrned plastic top panel isbonded directly to the bubble in the flat areas. This bond isaccomplished during the curing operation. Communication is thusestablished to or between the separate bubbles through the major andminor corrugations. With respect to the edge seal, the sides of thebubble are bonded directly to the pre-sanded top panel during the curingoperation. The resin in the uncured bubble layup acts as an adhesive.

The composition of the bubble or lower panel 20 is the same as the upperplastic panel. The surface is preferably crinkle but can be smooth withor without use of a facing plastic sheet such as Tedlar, Mylar or thelike. For fabrication of the bubble, see the step-by-step process givenabove. The thickness of the lower panel is preferably approximately0.035 inch, but can be varied. Glass fiber reinforcements are employedand the resin is preferably polyester but can be other plasticsubstances. Air bleed holes are provided at suitable locations. One suchair bleed hole may be seen in each panel bubble of FIG. 1 at the lowerright center of each.

Various types of sealants may be employed, but a typical example wouldhave as a base, 30 percent minimum, a blend of polybutylene, butyl and/or equal suitable compatible ingredients. Asphalt or asphalt derivativeswould preferably not be employed. As fillers, a 70 percent maximum,asbestos and other inert pigments would be employed.

Tedlar is a Du Pont trade name for polyvinyl fluoride. Mylar is a tradename for polyester.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure. 7

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim:

1. A light transmitting heat insulating panel construction for use inbuildings comprising a first outer light transmitting plastic sheet,said outer sheet substantially rectangular in shape with elongateparallel side edges and parallel end edges extending normal thereto, theside edges of the said outer sheet having partial major corrugationstherein and therealong whereby to permit side edge end engagement ofsaid sheet with the side and end edges of building panel sheets of likeconfiguration, the said outer sheet partial edge corrugations eachhaving an inner, stepped, base portion, and an inner second lighttransmitting plastic sheet also substantially rectangular in shape, saidsecond sheet of both lesser length and width than said first sheet andhaving upwardly dished side and end edges thereon, the upper extremitiesof said side and end edges of said second sheet bonded to theundersurface of said first sheet in substantially continuous manner, thelongitudinal side edges of said inner sheet integrally bonded to theinner, stepped base portion of the said outer sheet partial edgecorrugations, and the end edges of the second sheet inwardly spaced fromthe end edges of the first sheet whereby to permit end edge overlapengagement with like outer sheets.

2. A construction as in claim 1 wherein said inner second sheet issealingly bonded transversely thereof to the underside of said firstsheet intermediate the ends of the latter.

3. A light transmitting heat insulating panel construction for use inpanel wall and roof buildings comprising a pair of light transmittingplastic sheets of substantially rectangular form, the outside of saidsheets having inwardly stepped partial. side edge corrugations adaptingsame for side edge and longitudinally aligned end edge overlapengagement of other like outside sheets, said outside sheet alsomultiply and longitudinally corrugated inwardly of said side edgepartial corrugations thereof, the inner of said pair of sheets dishedcentrally and sealingly connected at its side edges to the inwardlystepped portions of the partial side edge corrugations of said outersheet and at the end edges thereof substantially inwardly of the endedges of said outer sheet, that said outer sheet free end edge portionsmay overlap like end edges of like outer sheets for connectiontherewith, whereby to provide a double walled sheet construction over asubstantial portion of the inner face of said outer sheet, the air spacebetween said two sheets substantially air tight.

References Cited UNITED STATES PATENTS 2,858,734 11/1958 Boyd 52-200 X2,918,023 12/1959 Bettcher 52639 X 3,124,224 3/1964 Paul et a1. 522083,127,699 4/1964 Wasserman 52-200 X 3,163,961 1/1965 Kemp 52-619 X3,265,556 8/1966 Hungerford et al. 16l-l89 FOREIGN PATENTS 74,85810/1952 Denmark.

999,697 10/ 1951 France.

526,115 9/1940 Great Britain.

277,185 10/ 1964 Netherlands.

DAVID J. WILLIAMOWSKY, Primary Examiner.

DENNIS L. TAYLOR, Examiner.

1. A LIGHT TRANSMITTING HEAT INSULATING PANEL CONSTRUCTIONS FOR USE INBUILDING COMPRISING A FIRST OUTER LIGHT TRANSMITTING PLASTIC SHEET, ANDOUTER SHEET SUBSTANTIALLY RECTANGULAR IN SHAPE WITH ELONGATED PARALLELSIDE EDGES AND PARALLEL END EDGES EXTENDING NORMAL THERETO, THE SIDEEDGES OF THE SAID OUTER SHEET HAVING PARTIAL MAJOR CORRUGATIONS THEREINAND THEREALONG WHEREBY TO PERMIT SIDE EDGE END ENGAGEMENT OF SAID SHEETWITH THE SIDE AND END EDGES OF BUILDING PANEL SHEETS OF LIKECONFIGURATION, THE SAID OUTER SHEET PARTIAL EDGE CORRUGATIONS EACHHAVING AN INNER, STEPPED, BASE PORTION, AND AN INNER SECOND LIGHTTRANSMITTING PLASTIC SHEET ALSO SUBSTANTIALLY RECTANGULAR IN SHAPE, SAIDSECOND SHEET OF BOTH LESSER LENGTH AND WIDTH THAN SAID FIRST SHEET ANDHAVING UPWARDLY DISHED SIDE AND END EDGES THEREON, THE UPPER EXTREMITIESOF SAID SIDE AND END EDGES OF SAID SECOND SHEET BONDED TO THEUNDERSURFACE OF SAID FIRST SHEET IN SUBSTANTIALLY CONTINUOUS MANNER, THELONGITUDINAL SIDE EDGES OF SAID INNER SHEET INTEGRALLY BONDED TO THEINNER, STEPPED BASE PORTION OF THE SAID OUTER SHEET PARTIAL EDGECORRUGATIONS, AND THE END EDGES OF THE SECOND SHEET INWARDLY SPACED FROMTHE END EDGES OF THE FIRST SHEET WHEREBY TO PERMIT END EDGE OVERLAPENGAGEMENT WITH LIKE OUTER SHEETS.